(1) Field of the Invention
This invention relates to a semiconductor wafer transport method and a semiconductor wafer transport apparatus using the same, and in particular to a technique for efficiently transporting semiconductor wafers formed thin.
(2) Description of the Related Art
Conventionally, semiconductor wafers to be processed are transported through different processing steps as follows.
Semiconductor wafers (hereinafter called “wafers” as appropriate) with patterns formed on front surfaces thereof have the back surfaces ground (back grinding). At this time, the wafers have protective tape applied to the front surfaces.
Each wafer, after the back grinding process, is transported as suction-supported at the back surface to each stage.
In the case of a semiconductor wafer mounting apparatus, for example, a wafer taken out of a cassette by a robot arm is placed on and suction-supported by an alignment stage. An aligning operation is performed for this wafer. The wafer removed from the alignment stage after the alignment is transported to a wafer mounting step, placed in the center of a ring-shaped frame and has the front surface sucked by vacuum. In this state, dicing tape is applied to the back surface to join the ring-shaped frame and wafer together.
In recent years, however, the semiconductor wafer has been tending toward reduced thickness to meet requirements for high density mounting. The semiconductor wafer formed thin presents the following inconveniences.
The wafer formed thin by back grinding has reduced rigidity due to a processing stress. This wafer becomes warped only by a slight stress applied to its surface from outside.
When the warped wafer is placed on an alignment stage, a faulty suction will occur in which only part of the wafer is sucked. The wafer remaining defectively sucked will be displaced during transport to a next processing step. In this state, the wafer cannot be placed accurately on a support table or the like for executing the next step.